This invention relates to an improvement of an armature which comprises a number of winding conductors, or half coils, which are printed on both surfaces of an insulating disc by etching or punching, the half coils on both surfaces of the disc being electrically connected to one another to form complete coils.
A typical conventional armature of this type is as shown in FIG. 1. Permanent magnets or magnetic poles 2 and magnetic members 3 are fixedly secured to a frame 1. A rotor 7 mounted on a rotary shaft 8 is provided in the space between the magnetic poles 2 and the magnetic members 3. The rotor 7 has an insulating disc 4 on both surfaces of which conductors 5 and 6 are printed. Current is applied to the conductors 5 and 6 through brushes 9.
Each of the conductors 5 and 6, as shown in FIG. 2, is made up of a radially extended linear conductor 11, and an inner sloped conductor 12 and an outer sloped conductor 13 which are extended from the ends of the linear conductor 11 towards the inner circumference and the outer circumference of the disc 4, respectively. In this armature, the width of each of the sloped conductors, especially the width W of the inner sloped conductor 12 is small, and therefore the current density therein is high.
In order to overcome this difficulty, a method has been proposed in the art in which each of the sloped conductors 12 and 13 is formed along an involute line (A.sub.1 or A.sub.2 in FIG. 3) with a circle R1 as its base circle, which is formed by the inner ends of the winding conductors, whereby the conductors are made uniform in width. According to the method, the effective conductor width is increased, the conductors are uniform in width, and accordingly the current capacity is increased, because the conductors are formed along the involute line of the circle.
On the other hand, recently it has been demanded especially for a small electric motor to decrease the armature current and yet to increase the torque constant. In order to satisfy this demand, it is necessary to effectively utilize the magnetic flux of the permanent magnets, i.e. to increase the magnetic flux effective area. However, the aforementioned method in which the sloped conductors are formed along the involute line with the circle formed by the inner ends of the winding conductors as its base circle is disadvantageous in that the magnetic flux effective area is defined by the inside diameter R1 and the outside diameter R2 of the winding assembly.